* [PATCH 4.15 105/122] nospec: Allow index argument to have const-qualified type [not found] <20180307191729.190879024@linuxfoundation.org> @ 2018-03-07 19:38 ` Greg Kroah-Hartman 2018-03-07 19:38 ` Greg Kroah-Hartman 0 siblings, 1 reply; 2+ messages in thread From: Greg Kroah-Hartman @ 2018-03-07 19:38 UTC (permalink / raw) To: linux-kernel Cc: Greg Kroah-Hartman, stable, Rasmus Villemoes, Dan Williams, Linus Torvalds, Andy Lutomirski, Arjan van de Ven, Borislav Petkov, Dave Hansen, David Woodhouse, Josh Poimboeuf, Peter Zijlstra, Thomas Gleixner, Will Deacon, linux-arch, Ingo Molnar 4.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Rasmus Villemoes <linux@rasmusvillemoes.dk> commit b98c6a160a057d5686a8c54c79cc6c8c94a7d0c8 upstream. The last expression in a statement expression need not be a bare variable, quoting gcc docs The last thing in the compound statement should be an expression followed by a semicolon; the value of this subexpression serves as the value of the entire construct. and we already use that in e.g. the min/max macros which end with a ternary expression. This way, we can allow index to have const-qualified type, which will in some cases avoid the need for introducing a local copy of index of non-const qualified type. That, in turn, can prevent readers not familiar with the internals of array_index_nospec from wondering about the seemingly redundant extra variable, and I think that's worthwhile considering how confusing the whole _nospec business is. The expression _i&_mask has type unsigned long (since that is the type of _mask, and the BUILD_BUG_ONs guarantee that _i will get promoted to that), so in order not to change the type of the whole expression, add a cast back to typeof(_i). Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-arch@vger.kernel.org Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/151881604837.17395.10812767547837568328.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- include/linux/nospec.h | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/include/linux/nospec.h +++ b/include/linux/nospec.h @@ -72,7 +72,6 @@ static inline unsigned long array_index_ BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \ BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \ \ - _i &= _mask; \ - _i; \ + (typeof(_i)) (_i & _mask); \ }) #endif /* _LINUX_NOSPEC_H */ ^ permalink raw reply [flat|nested] 2+ messages in thread
* [PATCH 4.15 105/122] nospec: Allow index argument to have const-qualified type 2018-03-07 19:38 ` [PATCH 4.15 105/122] nospec: Allow index argument to have const-qualified type Greg Kroah-Hartman @ 2018-03-07 19:38 ` Greg Kroah-Hartman 0 siblings, 0 replies; 2+ messages in thread From: Greg Kroah-Hartman @ 2018-03-07 19:38 UTC (permalink / raw) To: linux-kernel Cc: Greg Kroah-Hartman, stable, Rasmus Villemoes, Dan Williams, Linus Torvalds, Andy Lutomirski, Arjan van de Ven, Borislav Petkov, Dave Hansen, David Woodhouse, Josh Poimboeuf, Peter Zijlstra, Thomas Gleixner, Will Deacon, linux-arch, Ingo Molnar 4.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Rasmus Villemoes <linux@rasmusvillemoes.dk> commit b98c6a160a057d5686a8c54c79cc6c8c94a7d0c8 upstream. The last expression in a statement expression need not be a bare variable, quoting gcc docs The last thing in the compound statement should be an expression followed by a semicolon; the value of this subexpression serves as the value of the entire construct. and we already use that in e.g. the min/max macros which end with a ternary expression. This way, we can allow index to have const-qualified type, which will in some cases avoid the need for introducing a local copy of index of non-const qualified type. That, in turn, can prevent readers not familiar with the internals of array_index_nospec from wondering about the seemingly redundant extra variable, and I think that's worthwhile considering how confusing the whole _nospec business is. The expression _i&_mask has type unsigned long (since that is the type of _mask, and the BUILD_BUG_ONs guarantee that _i will get promoted to that), so in order not to change the type of the whole expression, add a cast back to typeof(_i). Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-arch@vger.kernel.org Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/151881604837.17395.10812767547837568328.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- include/linux/nospec.h | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/include/linux/nospec.h +++ b/include/linux/nospec.h @@ -72,7 +72,6 @@ static inline unsigned long array_index_ BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \ BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \ \ - _i &= _mask; \ - _i; \ + (typeof(_i)) (_i & _mask); \ }) #endif /* _LINUX_NOSPEC_H */ ^ permalink raw reply [flat|nested] 2+ messages in thread
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2018-03-07 19:38 ` [PATCH 4.15 105/122] nospec: Allow index argument to have const-qualified type Greg Kroah-Hartman
2018-03-07 19:38 ` Greg Kroah-Hartman
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